Digital world22 February 2014

Control valves may not be renowned for their rapid development, but actuators and positioners are continuing the transformation.

Modern 'smart' control valve units can make a considerable difference to both the efficiency and cost of plant operations – and it's not only about diagnostics and wireless. French fruit syrup manufacturer Teisseire, for example, which last year saw a significant investment in process equipment at its Crolles plant, reports improved performance thanks to implementing Bürkert 8681 pneumatic control heads.

These radically altered how process valves at the plant were controlled and actuated. In effect, traditional direct air connections to control cabinets were eliminated, with the plant instead using intelligent fieldbus-connected devices. Marc Klingler, hygienic segment manager at Bürkert, says the new system has increased both the reliability and efficiency of Teisseire's 300,000-550,000 litres per day production line, while also helping to reduce maintenance stores inventory.

How? He recalls that the previous valve control system was 15 years old and consisted of a mix of control heads, some manual, some automated, but not interacting well together. As part of the upgrade, site engineers decided to move to a decentralised automation approach, with the new control heads taking over all pneumatic actuation, feedback and diagnostics up to and including fieldbus communication – and linking to all control valve types.

Klingler explains that the new approach offered several advantages. By mounting the control heads directly onto control valves, for example, both the length and the total number of connections were reduced, simplifying project planning, installation, commissioning and maintenance. Also, with much shorter air lines, both switching times and air consumption were minimised, improving plant reliability.

In fact, the process valve switching positions are now detected by an inductive, analogue position sensor and reported to the plant's PLC-based automation system. Klingler says that up to three switching points can be adjusted automatically by a Teach-In facility, and that the valves are easy to set up using the system's ProcessTune function. The control head also eliminates any risk of contamination thanks to its hygienic design, while maintenance is facilitated by Bürkert's patented external magnetic activation.

It's a different world out there. And while control valves themselves may not be developing so spectacularly, digital valve actuator-positioners are also part of the revolution. Look at Emerson Process Management's Fisher Fieldvue digital valve controller, for instance, which is now claimed to fit any valve type (single acting, double acting, rotary, linear and emergency shutdown) from any manufacturer.

Astonishingly, Fieldvue, with its early digital fieldbus communications and diagnostics, was introduced a full two decades ago. Indeed, despite slow initial uptake, it recently passed the 1.5-million mark sold and is now widely credited with improving operations and maintenance as well as accelerating this sector's move to valve-related digital instrumentation.

"Fieldvue instruments have become the industry standard and have made Emerson the market leader in the digital control of valve operation, diagnostics and predictive maintenance," says Bruce Grumstrup, Emerson's vice president for Fieldvue and positioning instruments. "Today, the capabilities of the Fieldvue family of instruments have become extremely diverse, including nuclear-certified, natural gas approved, remote mount and safety-instrumented systems," he adds.

In fact, Emerson is far from alone here. Look no further than ABB's PositionMaster EDP300 electro-pneumatic positioner and Siemens' SiPart PS2 digital positioners, the latter also claimed to be universal, including in terms of fieldbus connectivity. But do plants actually use the connectivity and resulting diagnostics, or simply buy the kit, because that's what's available?

It's doubtless a mix, but wireless technology is improving uptake, according to Richard Grace, product manager for Emerson's Fisher Instruments business. "We're hitting a steep climb on the [adoption] curve," he insists. "We've had Wireless HART for four years and a lot are now using it day-to-day. They're seeing useful applications they can set up wirelessly."

And in doing so, they're no longer held back by ageing plant infrastructures. "Many haven't been able to make use of the diagnostics from the field, because their control systems couldn't access the data. But the beauty of wireless is that they can access the information directly from the devices into their asset management systems."

Now that's smart.

Brian Tinham

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